1. Field of the Invention
The present invention relates to a liquid crystal display substrate and a method of manufacturing it and more specifically to a liquid crystal display substrate incorporating thin-film transistors, which serve as switching elements, and a method of manufacture thereof.
2. Description of the Prior Arts
A so-called active matrix type liquid crystal display substrate has nonlinear elements (switching elements) provided in one-to-one correspondence to a plurality of pixel electrodes arranged in the form of a matrix. The liquid crystal at each pixel is theoretically driven at all times (duty ratio of 1.0), so that the active type has better contrast than a so-called simple matrix type that adopts a time-division driving method. The active matrix type liquid crystal display substrate is becoming an essential technology particularly for color liquid crystal display devices. A representative switching element is a thin-film transistor (TFT).
The thin-film transistor consists of: a gate, a gate insulating film and a silicon layer such as an amorphous silicon (a-Si) layer or polysilicon (p-Si) layer, all formed successively on the surface of a transparent substrate in which pixel electrodes are formed; and a drain electrode and a source electrode, both deposited on the silicon layer and formed integral with an interconnect layer or busline that supplies voltage and also with pixel electrodes.
The liquid crystal display substrate of the active matrix type using the thin-film transistors is known and introduced in such publications as Japanese Patent Laid-Open No. 309921/1988 and an article entitled "12.5-type Active Matrix Color Liquid Crystal Display Using Redundant Configuration" in Nikkei Electronics, page 193-210, Dec. 15, 1986, published by Nikkei McGraw-Hill.